Why do Americans say "erbs" instead of "herbs"? (idea)

There is a simple explanation, it's called a dialect. There are certain differences in the same language in certain areas of the world. It's not to be pretentious, or arrogant; it simply evolved over a period of time. You can find lots of dialects just inside of the U.S.: southern, west coast, east coast, mid-west, and so on. Have you ever heard someone say, "That person has a southern drawl."? Well that is because that person speaks a variation of a widely used langauge. Here in the U.S., most people think that the way Europeans pronounce some words is odd, so it goes both ways.